Using Goal.com's Ratings Index, which takes every player's top-flight displays into account, we take a look at the worst performers of the 2012-13 campaign so far

While pre-season expectations have been met thus far by many of the Premier League's top stars, others have not fared as well. Wayne Rooney, Robin van Persie, Luis Suarez & Co. continue to deliver at the highest level, but some players a little further down the league have failed to get to grips with the 2012-13 campaign. So, using our unique Ratings Index, which takes every Premier League performance into account, we take a look at the worst players in the top flight so far this season...

Having been linked with Arsenal and Liverpool after Wigan's impressive start to the season, it has been quite a downfall for goalkeeper Ali Al-Habsi. The Oman international earned rave reviews early on in the campaign but has been at fault for goals on a number of occasions since as Roberto Martinez's men slipped from genuine top-10 contenders to relegation material.

Dubbed 'the next Paolo Maldini' when he broke through at Inter in 2008, Davide Santon has failed to live up to such hype in the Premier League this season. Like many of his Newcastle team-mates, the full-back is yet to find the kind of form that helped the club seal a shock fifth-placed finish last year and is a shadow of the player that was performing so well when he arrived in English football.

The summer signing of James Collins and impressive form of Winston Reid at West Ham has hampered the progress of James Tomkins. The 23-year-old was named in the PFA Championship Team of the Year as the Hammers won promotion via the play-offs last term but he has so far been unable to regain his preferred centre-back position and has struggled when called upon by Sam Allardyce in midfield.

You can forgive a player for trying too hard to make a good impression on their Premier League debut, but Ivan Ramis' rash first seven minutes in a Wigan shirt provides the perfect example of how not to make yourself known. The Spanish centre-back, a summer signing from Mallorca, was at fault for both Chelsea goals in a 2-0 defeat on the opening weekend of the season, and has been part of a Latics defence that has already conceded 32 goals in 17 matches.

A whirlwind 2012 has seen Ryan Bertrand win the FA Cup, Champions League, England caps and a regular place in the Chelsea first team, but his performances in the Premier League this season have been far from convincing. The 23-year-old is yet to impress when deputising for Ashley Cole at left-back and has been ineffective when deployed on the left of midfield.

QPR looked to have pulled off a coup with the signing of Shaun Wright-Phillips from Manchester City at the start of last season. Neither Neil Warnock or Mark Hughes, who the winger had recaptured his form under at City two years previously, were able to get the best out of him again, though, and his steady decline has continued at Loftus Road this campaign.

A serious ankle injury cut Gary O'Neil's Premier League return short after he joined West Ham from Middlesbrough in January 2011. Despite impressing in the Championship as he made his long-awaited comeback towards the end of last season, he has been outshone by fellow midfielders Mohamed Diame, Mark Noble and Kevin Nolan, and is yet to prove he still has what it takes at the top level.

A nailed-on starter for Manchester United in 'big games' in recent seasons, a lot was expected of Park Ji-Sung when he made the move to QPR in the summer. The South Korean was given an important role in the centre of midfield and named captain upon his arrival, but he has not bounced back from a dismal performance against Swansea on his debut and is now sidelined through injury.

It took until November 10 for a Sunderland player other than Steven Fletcher to find the target in the Premier League, with Stephane Sessegnon failing to ease the goal burden on the club's £12 million summer signing. The Benin international's form has picked up in recent weeks but his early-season showings summed up what has been a below-par campaign thus far for the Black Cats.

Brendan Rodgers said he would not have allowed Andy Carroll to leave Liverpool if he knew a replacement would not be brought in, but the striker has hardly shown his boss what he is missing out on with a slow start to his loan spell at West Ham. Injuries have restricted the £35m England international to just nine Premier League starts for the Hammers and a lack of form has seen him score just once this season.

Signed for £4.6m from Sochaux in the summer, Modibo Maiga had looked set to challenge Carlton Cole for the lone striker role at West Ham. However, the surprise arrival of Carroll late in the transfer window means the Malian's chances have been limited, and even when he has been given an opportunity to prove his worth he has failed to take it. Marseille have been linked with a January move for the forward.